The Cine Technician (1935-1937)

86 The Journal of the Association of Cine-Technicians Dec, 1936J an., 1937 Some Recent Developments in Sound Recording Equipment W. H. CLARKE (of R.C.A. Photophone Ltd.) The following is a paper read by Mr. Clarke to the Association of CineTechnicians, November 5th, 1936. The original numbering of the figures, several of which are reproduced, has been retained. Summary. By the frequent introduction of new apparatus for sound recording and reproducing work, Equipment Manufacturers are applying the full resources of their Research staffs to improve the quality of sound films presented to the public. In this connection development has proceeded along the lines of improved pick-up devices, constant speed mechanisms for recording and scanning, improved optical systems and light modulating units, extension of frequency range, more elaborate and exact monitoring devices, the further reduction of ground noise, improved resolution of film emulsions and the elimination of distortions emanating from development and printing. Method of attack on the many problems involved has been facilitated by the constructive criticisms provided by technicians in the field and the personnel of plant, which is closely allied in eventually providing the finished recordings. J CHAHACTEPISTIC IHOPHOME TYPE 44A This paper is presented with the object of bringing before you development which is to be put into practical form in the near future. The apparatus under construction by R.C.A. Photophone is providing for an imiiroved microphone— a new type printer — a means of obtaining a more clearly defined sound track by means of ultra violet exposures, and a method of further reducing ground noise and increasing volume range. In covering the.se developments, mention must be made of the Neon Volume Indicator, and Uni-directional Microphone, although several members present may already be fairly familiar with both units. Uni-Directional Microphone. The Uni-directional Microphone has been developed as a sequel to the bi-directional ribbon, and as a practical answer to the request of prominent studio engineers for a device which would permit sound waves to be collected from the required direction only. The bi-directional microphone, with its well-known figure 8 response characteristic, achieved the dual purpose of rejecting unwanted reflected waves and incidental noises from two directions, and, at the same time, increased the distance at which the microphone could be used from the origin of the incident wave. Such an improvement in pick-up sensitivity without increased reverberation was a decided advantage in dialogue recording and of great benefit when balancing for orchestral work. However, in sound film recording the second zone of equal sensitivity differing from the first zone by 180° couM become a source of inconvenience under certain conditions of action. The uni-directional property of the new microphone is obtained by combining the characteristics of a pressure operated unit and a velocity operated unit. The essential parts are shown in Figure 2, and in practice use is made of a single ribbon, the upper part of which is pressure operated and the lower part velocity operated. The, resultant collecting area of such a combination is shewn in Figure 3, which gives the directional characteristic at several frequencies. For dialogue recording the wide angle of the microphone shews very little attenuation of signal strength at all frequencies. For example, the attenuation at 60° either side of 0° is about 2-5 db, while the directional property is Figure 2. A dis-assembled view of the Typo 77-.\ microplione. Note particularly the pipe which encloses the rear of the upper (pressure-actuated) half of the ribbon, and the ingeniously arranged labyrinth which furnishes the proper acoustic termination for the pipe.